Abstract
ABSTRACT Phomopsis seed decay (PSD) of soybean ( Glycine max L. Merr) is primarily caused by Phomopsis longicolla. Currently, percent seed infection is used as a method for evaluating resistance to PSD. However, researchers need a common system for classifying soybean genotypes for their reaction to P.longicolla that is consistent across environments. The purpose of this research was: (i) to evaluate the reaction of a select set of soybean accessions to P. longicolla, and (ii) determine the effects of irrigation and two harvest regimes (normal and delayed) on seed infection. We propose a classification system for comparing reactions to P. longicolla among accessions based on a Phomopsis seed infection index (PSII), derived by dividing the percent seed infection of each accession by percent seed infection values of susceptible standards selected within early and late maturity groups. Percent seed infection by P. longicolla infection was greater when accessions were irrigated during the growing season and harvested at normal maturity. Some lines such as MO/PSD‐0259 were rated as resistant to P. longicolla (7% seed infection) when not irrigated and harvested at maturity, but were rated as susceptible (39% seed infection) with irrigation and delayed harvest. The resistance ratings to P. longicolla using percent seed infection and PSII varied among accessions. SS93–6012, for example, had similar ratings for both (9% seed infection and 16% PSII). PI 416942 exhibited some resistance to P. longicolla based on percent seed infection (8%), but no resistance based on PSII (32%). Accessions PI 594478, Delmar, SS93–6012, SS93–6181, PI 594603A, and PI 594712 were classified by PSII as moderately resistant under irrigation and with delayed harvest. These results indicate that simple comparisons of percent seed infection among accessions without irrigation, without delayed harvest, and without a standard control of a similar maturity group might result in false conclusions about resistance to P. longicolla .
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Claims 9
Claim · model-written summary
Soybean accessions had greater P. longicolla seed infection when irrigated and harvested at normal maturity.
- Taxon
- accessionse0
- Treatment
- irrigated during the growing season and harvested at normal maturitye0
- Interactor
- P. longicollae0pathogen
- Outcome
- Percent seed infectione0
- Direction
- greatere0
Not reportedComparator
Verbatim
e0“Percent seed infection by P. longicolla infection was greater when accessions were irrigated during the growing season and harvested at normal maturity.”
Claim · model-written summary
MO/PSD‐0259 was rated resistant with 7% seed infection without irrigation at maturity.
Verbatim
e0“MO/PSD‐0259 were rated as resistant to P. longicolla (7% seed infection) when not irrigated and harvested at maturity”
Claim · model-written summary
MO/PSD‐0259 was rated susceptible with 39% seed infection under irrigation and delayed harvest.
Verbatim
e0“MO/PSD‐0259 were rated as resistant to P. longicolla (7% seed infection) when not irrigated and harvested at maturity, but were rated as susceptible (39% seed infection) with irrigation and delayed harvest”
Claim · model-written summary
Resistance ratings from percent infection and PSII varied among soybean accessions.
Verbatim
e0“The resistance ratings to P. longicolla using percent seed infection and PSII varied among accessions.”
Claim · model-written summary
SS93–6012 had similar ratings by seed infection and PSII, at 9% infection and 16% PSII.
Verbatim
e0“SS93–6012, for example, had similar ratings for both (9% seed infection and 16% PSII).”
Claim · model-written summary
PI 416942 showed some resistance by percent seed infection at 8%.
Verbatim
e0“PI 416942 exhibited some resistance to P. longicolla based on percent seed infection (8%)”
Claim · model-written summary
PI 416942 showed no resistance by PSII at 32%.
Verbatim
e0“PI 416942 exhibited some resistance to P. longicolla based on percent seed infection (8%), but no resistance based on PSII (32%).”
Claim · model-written summary
Six named accessions were moderately resistant by PSII under irrigation and delayed harvest.
Verbatim
e0“Accessions PI 594478, Delmar, SS93–6012, SS93–6181, PI 594603A, and PI 594712 were classified by PSII as moderately resistant under irrigation and with delayed harvest.”
Claim · model-written summary
The authors warn that infection comparisons lacking irrigation, delayed harvest, and maturity-matched standards may misclassify resistance.
Verbatim
e0“simple comparisons of percent seed infection among accessions without irrigation, without delayed harvest, and without a standard control of a similar maturity group might result in false conclusions about resistance to P. longicolla”